1. Field of Invention
The present invention relates generally to the field of oilfield exploration, production, and testing, and more specifically to deflector apparatus commonly known as whipstocks comprising degradable compositions, and methods of using same.
2. Related Art
Existing structural compositions, that is materials and combinations of materials, have been developed to sustain elevated loads (forces, stresses, and pressures) at useful ranges of temperatures, and also not to react, and thus degrade by dissolving, disintegrating, or both in the presence of common fluids such as water, or moist air. Note, for a better understanding of the invention, that a composition is here defined as a tangible element created by arranging several components, or sub-compositions, to form a unified whole; the definition of composition is therefore expanded well beyond material chemical composition and includes all combinations of materials that are used smartly to achieve the purposes of the invention.
Structural compositions found in everyday applications (mainly metals and alloys) are required to be durable over intended element lifetimes; i.e. they must be chemically inert, or not reactive, even though many rust or corrode over the intended element lifetimes. In generic terms, a reactive metal may be defined as one that readily combines with oxygen to form very stable oxides, one that also interacts with water and produces diatomic hydrogen, and/or one that becomes easily embrittled by interstitial absorption of oxygen, hydrogen, nitrogen, or other non-metallic elements. There are clearly various levels of reactivity between metals, alloys, or in general compositions, or simply any element listed on the periodic table. For instance, compared to iron or steels (i.e. alloys of iron), aluminum, magnesium, calcium and lithium are reactive; lithium being the most reactive, or least inert of all four. Reactive metals are properly grouped in the first two columns of the Periodic Table of the Elements (sometimes referred to as Column I and II elements); i.e., among the alkaline and alkaline-earth elements. Of the alkaline metals, namely lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), francium (Fr), and alkaline-earth metals, namely beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), radium (Ra), few may be directly utilized for the excellent reasons that they are either 1) far too reactive to be handled safely and thus be readily procurable to be useful for any commercial applications, or 2) not sufficiently reactive as they for instance passivate in aqueous environments and thus form stable protective barriers (e.g. adherent oxides and hydroxide films), or 3) their rate of reaction or transformation, and thus degradation, is too slow, as it is for instance seen when magnesium, aluminum and their commercial alloys are immersed in cold and neutral water (i.e. neither acidic nor basic; pH=7). Though profoundly less reactive than the alkaline and alkaline-earth metals, aluminum may be also included among the reactive metals. Yet, aluminum does not react, or degrade with water nearly to the same extents as the Columns I and II elements since aluminum is a typical material used in durable elements for applications as diverse as automotive, aerospace, appliances, electrical, decoration, and the like. To quantify reactivity of an element, galvanic corrosion potentials may be used, or if unavailable measured, as for instance for any novel composition compared to a reference, for instance the hydrogen reaction; for instance the higher the potential of a composition with respect to hydrogen the lesser its reactivity and its likelihood to degrade noticeably, or rapidly. Because reactivity of an element is linked to the ease chemical reactions proceed with non-metallic elements (e.g. oxygen, nitrogen), for periodic table elements electronegativity constitutes an excellent measure of reactivity. Electronegativity, and especially corrosion potential of aluminum are sufficiently low compared to the other elements of the periodic table to categorize aluminum as a reactive metal rather than a non-reactive, inert or noble metal or element.
In the oilfield environment, it would be advantageous to be able to utilize a whipstock or deflector component comprised of a reactive composition comprising alkaline, alkaline-earth elements, or other metal (e.g. aluminum) having either an enhanced reactivity (e.g. compositions comprising aluminum) or reduced reactivity (e.g. compositions comprising calcium) relative to that of the (pure or unalloyed) alkaline or alkaline-earth elements in the composition. Whipstocks and deflectors are currently used as a means to deflect assemblies and tools into a lateral section of a multilateral wellbore. They are currently made using non-degradable components. These devices must be retrieved with a separate trip in the well, which is added cost. So in some cases, the deflector or whipstock is left in the hole (to save cost) and production is brought online. However, the presence of the devices in the main bore means reduced flow area. It would also be of great benefit to controllably enhance or delay the interaction or degradation of the whipstock or deflector with its fluidic environment; an environment that may comprise water, completion fluids, and the like and will therefore be corrosive to the whipstock or deflector. The compositions of interest are those that degrade by either dissolving or disintegrating, or both when demanded by the application or the user. The degradation may proceed within minutes, hours, days or weeks depending upon the application requirements; in oilfield environments typical time for degradation may range from minutes to days, occasionally weeks.
In many well operations it is thus desirable to possess and use whipstock and deflectors that controllably degrade either in rate, location of the element, or both (or include a portion that predictably degrades) in the wellbore environment, without having to resort to highly acid conditions, high temperatures, mechanical milling, or a combination of these. Since none of the known diverters and whipstocks have the ability to degrade in a controlled user defined fashion, such degradable elements could potentially be in high demand in both the oilfield.